In a conventional moving coil type actuator, a coil unit is disposed between magnets, which are provided at central and outer positions in a casing. The coil unit is coupled to an actuating rod, and the actuating rod is supported by a bearing member. A load is coupled to an end of the actuating rod. When electricity is supplied to the coil unit, magnetic force lines perpendicular to electric force lines of the coil unit are formed by the magnets. Force is applied to the coil unit in a direction perpendicular to a plane containing both the magnetic force lines and the electric force lines, which are perpendicular to each other. As a result, the actuating rod is moved, thus moving the load coupled thereto.
In such a conventional moving coil type actuator, the direction in which the actuating rod is moved is changed by converting the direction of electricity applied to the coil unit. The speed at which the actuating rod is moved is controlled by adjusting the intensity of electricity applied to the coil unit.
However, in the conventional moving coil type actuator, the coil unit and the actuating rod are supported only by a bearing member disposed in the casing, so that it is difficult to maintain the distances between the coil unit and the magnets constant. Hence, when electricity is applied to the coil unit, the movement of the coil unit is unstable. As a result, movement of the coil unit and the actuating rod may be nonlinear.
Furthermore, because the load is actuated by electric force applied to the coil unit and by force generated by the magnets, a very large electric force can be required to actuate a large load.